1. Field of the Invention
This invention relates to packaged shelf-stable (12 weeks or more under refrigerated conditions) cheese spreads having, as the sole or major cheese ingredient, a natural cheese which normally has a relatively short shelf-life, and a process for preparing same.
2. The Prior Art
A number of natural cheeses suffer the disadvantage of poor shelf-life, the principal cause being a relatively high water content thereby providing a suitable environment for continued (during storage) action of the naturally present enzymes. Because of their water content in relation to solids content and the degree of decomposition of the protein these cheeses can be classified in terms of body, or consistency, as soft, semi-soft or medium.
Typical soft cheeses (generally known as "soft ripened cheeses") are Camembert, Brie, Liederkranz and Romadour; all are characterized by extremely poor shelf-stability.
Those having semi-soft to medium consistencies have longer shelf lives than the soft-ripened cheeses, but nevertheless substantially shorter than the hard cheeses such as Cheddar, Emmenthal, Gouda, etc. Typical cheeses in this category are Limburger and the various "blue-veined" cheeses, the veins of which are produced by the mold Penicillium roqueforti, such as Roquefort, Stilton, Gorgonzola, Danish Bleu, and Blue cheese. Another cheese of this type is the "nuworld" cheese, developed at the University of Minnesota and the University of Wisconsin, U.S.A., which is ripened in the presence of a white mutant of Penicillium roqueforti. These white mutants, and the method of preparing same, are described in the paper entitled "White Mutants of Penicillium roqueforti" by S. G. Knight, W. H. Mohr and W. C. Frazier, J. Dairy Science 33 (1950) pp. 929-933. Nuworld cheese is extremely similar in consistency, texture and taste to the conventional "blue-veined" cheeses, the principal difference being that the veins of nuworld cheese are white rather than blue or blue-green.
For convenience, the above-described cheeses, characterized by soft to medium consistencies and poor shelf lives, will be referred to, throughout the specification and claims, as "natural, soft-to-medium cheeses".
Various techniques have been tried, and proposed, for increasing the storage stability of these cheeses, including the application of conventional processes for preparing "process cheese", but none of these techniques have been completely successful in obtaining products having both good shelf life and the characteristic flavor of the original cheese.
Process cheeses, having consistencies of soft to semi-soft, are conventionally prepared by starting with one, but more often two or more, hard cheeses, or at least one hard cheese plus a minor amount of one or more soft to medium cheeses, removing the rind or rinds if necessary, cutting, milling, adding an edible fat such as butter, plus water, to impart the desired final consistency, plus one or more emulsifying or stabilizing agents which are customarily phosphate or citrate salts, optionally sterilizing the mass at a high temperature (about 125.degree. C.-140.degree. C.), bringing the temperature to about 75.degree. C.-80.degree. C. and agitating at this temperature to produce the desired texture and consistency, and finally filling the process cheese mass into appropriate containers or packages. The process cheese techniques produce products having very good shelf stability, normally far greater than that of the original starting material cheese or cheeses. Problems are encountered, however, if such techniques are applied to a natural, soft-to-medium cheese or a mixture containing a large proportion of such a cheese. During the processing, and particularly during the milling step, these cheeses acquire an unworkable sticky consistency and become rancid, because of their high water contents and enzyme systems.